Transducers such as an actuator, a sensor, and a power generating device perform conversion between mechanical energy and electric energy. Another type of transducers such as a speaker and a microphone perform conversion between acoustic energy and electric energy. In order to form a highly flexible, compact, and lightweight transducer, polymer materials such as dielectric elastomers are useful.
For example, an actuator contains a dielectric layer formed of a dielectric elastomer and a pair of electrodes placed on both sides of a dielectric layer in the thickness direction. In the actuator, when a voltage applied between the electrodes is increased, an electrostatic attraction between the electrodes increases. The dielectric layer, placed between the electrodes, is thereby compressed in the thickness direction, leading to a reduced thickness of the dielectric layer. When the film thickness is reduced, the dielectric layer accordingly expands in a direction parallel to the electrode surfaces. On the other hand, when the voltage applied between the electrodes is reduced, the electrostatic attraction between the electrodes decreases. A compressive force applied to the dielectric layer in the thickness direction thereby decreases, and the film thickness increases due to the elastic restoring force of the dielectric layer. When the film thickness increases, the dielectric layer accordingly contracts in a direction parallel to the electrode surfaces. The actuator thus expands and contracts its dielectric layer, thereby actuates a member to be actuated.
In order to increase the force and displacement output from the actuator, it is preferable that the dielectric layer has a higher dielectric constant, higher resistance to dielectric breakdown, and higher flexibility. A higher dielectric constant allows the layer to accumulate more charges therein. Higher resistance to dielectric breakdown allows the layer to withstand a higher electric field. Higher flexibility allows the layer to be expanded and contracted repeatedly. A silicone rubber, which has high resistance to dielectric breakdown, and acrylic and nitrile rubbers, which have high dielectric constants, are frequently used to prepare the dielectric layer (see, for example, PTL1 and PTL2).